This invention relates generally to flexible packages, and more particularly to flexible packages for holding products in a hermetically sealed condition, e.g., isolated from the ambient atmosphere, while allowing a controlled amount of air into the package in order to provide a smooth aesthetically appearing surface.
Various types of flexible packages for holding particulate materials under vacuum therein have been disclosed in the patent literature and are commercially available today. Examples of packages for holding ground or whole bean coffee are found in the following U.S. Pat. Nos. 4,576,285, 4,705,174, and 4,913,561.
The major advantages of flexible packaging, as compared to relatively rigid packaging, e.g., cartons, are that until the flexible package is filled it takes up very little volume, and after it is emptied of its contents it readily collapses, thereby reducing its volume to approximately that of the unfilled package. The former characteristic is a significant advantage insofar as storage is concerned, while the latter characteristic is a significant advantage from the standpoint of disposability. One common type of flexible package for holding goods under vacuum until the package is opened is the so-called "gussetted" package or bag. Typically such a package is formed from a web of flexible stock material, e.g., polyethylene, polyester, polypropylene, metal foil, and combinations thereof in single or multiple plies, into a tubular body, having a face panel, a back panel, and a pair of gussetted sides. Each gussetted side is formed by a pair of gusset sections and a central fold edge interposed between a pair of outer fold edges. The lower end of the bag is commonly permanently sealed, e.g., heat sealed, along a line extending transversely across the width of the bag close to its bottom edge. The top of the bag is commonly sealed transversely across the entire width of the bag in a number of ways to maintain the contents under vacuum until the bag is opened. Such action is frequently accomplished via a readily openable mouth, which when opened provides access to the contents of the bag.
One-way degassing valves are typically included in flexible packages to enable any gasses produced by the particulate material within the package to exit from the package, while preventing air from entering into the package through the valve. Examples of such one-way degassing valves are shown in U.S. Pat. Nos. 3,595,467, 3,799,427 and 4,420,015.
One drawback of many commercially available vacuum sealed flexible packages is the fact that when the package is filled, sealed and evacuated the material forming the walls of the package intimately engages the particulate material disposed therein, thereby resulting in an uneven, bumpy, pebbly or otherwise less than satisfactory aesthetic appearance. In U.S. Pat. No. 4,727,706, which is assigned to the same assignee as this invention, there is disclosed a package which exhibits the advantages of hermetically sealed flexible packaging, yet provides a smooth aesthetically pleasing appearance. That package basically comprises an inner bag and an outer bag. The inner bag is formed of a flexible sheet material which is resistant to the passage of gas therethrough. The outer bag is also formed of a flexible sheet material. The outer bag is secured to the inner bag by adhesive areas which define passageways therebetween through which air from the ambient atmosphere may flow to enter the space between the outer and inner bags. The inner bag is arranged to be filled with a particulate material and then the bag vacuumized and sealed, whereupon the walls of the inner bag closely conform to the surface of the particulate material. The air space between the inner and outer bag enables the outer bag to have a smooth aesthetically pleasing appearance even though the inner bag may be in close conformance to the contents of the package.
It is not an uncommon practice by producers of other types of hermetically sealed flexible packages to perforate the package to release trapped air for stacking and shipping. This practice allows the air within the package to be expelled from the package to prevent the package from "pillowing." As will be appreciated by those skilled in the art, such pillowing is undesirable, particularly with relatively large packages, e.g., approximately twenty five pounds or more, since it can adversely affect the package's ability to be stacked in a stable manner, one on top of another. The disadvantage with perforating the hermetically sealed package is that it reduces, if not destroys, the effectiveness of the hermetic seal.
For many applications, e.g., packaging of agricultural chemicals or other industrial particulate materials, the hermetically sealed package can exhibit a pebbly or unsmooth appearance resulting from its evacuation and concomitant close conformance to its particulate contents, yet still be acceptable, since appearance of the packaging is typically not a factor in industrial applications. Where, however, relatively large packages of particulate materials are intended for personal or home use, e.g., large bags of dry pet foods, the appearance of the package becomes important insofar as marketability is concerned.
Accordingly, a need exists for packaging which is simple in construction, relatively low in costs, and which provides the advantages of conventional hermetically sealed packaging, while providing an aesthetically pleasing smooth external appearance.